Neural induction has been defined operationally, and the interacting tissues have been grossly identified, but the molecular mechanisms of neural induction are not known. The ultimate aims of this proposal are to define those mechanisms at cellular, molecular and genetic levels in the frog, Xenopus. The initial aim is to isolate components of the gastrula that have neural inductive potency which can be used as immunizing material for production of monoclonal antibodies. A novel method of retrieval of such material is used: a nitrocellulose filter is implanted in the dorsal blastopore lip region during neural induction. After about 4 hours the conditioned filter is removed and cut in half: piece (A) is tested for inductive potency by ventral implantation into an early gastrula (controls show that virgin nitrocellulose does not have an effect); piece B is stored frozen. If (A) proves to have neural inductive potency, (B) is used as immunizing material in mice that have been tolerized from birth by injections of ventral halves of Xenopus gastrulae (Hockfield 1987). The aim is to produce monoclonal antibodies that react specifically with components of the neural induction system attached to nitrocellulose filters. To identify these components, antibodies are screened on tissue sections of different stage Xenopus embryos, and by SDS PAGE and Western blotting. Antibodies are tested for their ability to block the neural induction potency of conditioned filters, and to block neural induction in vivo and in vitro, assayed by NCAM expression (Jacobson and Rutishauser 1986). Suitable antibodies are used to screen a Xenopus gastrula cDNA expression library, with the aim of identifying proteins involved in neural induction.